public class Test_String_tools {
    public static void main(String[] args) {
        String_tools st = new String_tools();
        System.out.println(st.concat('-'));
        System.out.println(st.concat('-',"hello"));
        System.out.println(st.concat('-',"hello","world"));
        System.out.println( st.concat('-',"hello","world","hsy"));
    }
}
